Automobile tires are finally prepared as composites of various materials, a primary component being rubber. Generally, various parts of the tires are prepared from different formulations in order to demonstrate optimum properties and their respective functions.
The tire tread of an automobile tire in addition to being the wear surface must also exhibit good skid resistance and, in particular, good wet skid resistance. It is also highly desirable to provide tire tread compositions capable of functioning well at low temperatures and having an improved resistance to stiffness or brittleness tendencies at such low temperatures, such as about 0.degree. F.
Rubbers which have been used in the manufacture of tire tread compositions include natural rubber and synthetic rubbers such as polyisoprene, styrene butadiene rubber (SBR), polybutadiene rubber (BR) as well as ethylene-propylene copolymers (EPM), ethylene-propylene-diene terpolymers (EPDM), butyl rubber copolymers as defined in U.S. Pat. No. 2,356,128, which contain 85-99.5% of combined C.sub.4 -C.sub.7 isoolefin and 0.5 to 15% of combined C.sub.4 -C.sub.14 multiolefin and chlorinated butyl rubbers containing 0.5 to 3.0 wt. % combined chlorine, as defined in U.S. Pat. No. 3,099,644. Symbols for rubber polymers used herein such as BR are defined in ASTM-D-1418-72a. Tires prepared from butyl rubber have been found to have better skid resistance than others, but wear properties are not completely adequate. Blends of chlorinated butyl rubber with SBR and BR do exhibit improved wet skid resistance but the wear properties are inferior to those of conventional tire tread compositions.